<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

<script>
    var a = 'username';

    var o = {
        username:'frank'
    };
    console.log(o['username']);
    console.log("**************")
    console.log(o['user'+'name']);
    console.log("**************")
    var arr = ['aa','bb','cc']
    for (var i = 0;i<arr.length;i++){
        console.log(arr[i])
    }




</script>
</body>
</html>